if we have four more years of president obama we can't wait four years for the economy to start growing. >> reporter: that may be resonating as the race tightening again in latest nbc news, "wall street journal" poll. romney is trailing by three points, within the margin of error. 46% of registered voters approve of the president's handling of the economy. 51% disapprove. top aides say the president's strategy tonight is to try to turn his weaknesses on the economy and deficit to strengths. by roughing up romney on the idea he will hurt the middle class. >> he says he will cut the deficit, please. he wants $2 trillion in new defense spending that the pentagon didn't ask for. $5 trillion tax cut, future of the wealthy. >> reporter: the claim is complicated by the way biden framed the argument. >> how they can justify raising taxes in the middle class has been buried the last four years. how in lord's name can they justify raising their taxes? >> obama officials today insisted that was not a gaffe, biden clarified. >> the middle class was buried by the policies of romney and ryan supporte